Pulverizing mills of the updraft type, often called "bowl mills," are commonly used to crush coarse material such as coal to prepare the coarse materials for subsequent operations. In the case of coal, coarse chunks or lumps of coal are pulverized into fines in preparation for use in the coal fired boilers of electric utility plants. An example of a rotating throat, updraft bowl mill can be found in U.S. Pat. No. 3,465,971 issued Sept. 9, 1969 to J. F. Dallenberg et al.
The materials, such as coal, which are pulverized or ground in the bowl mill are highly abrasive and tend to abrade or wear away the surfaces of the bowl mill which are contacted by them. The bowl mill, in addition to crushing or pulverizing the material, also performs a classifying or separating function in which heavy materials, such as pyrites, are separated out of the crushed coal and collected in a chamber beneath the crushing surface of the rotating bowl. The movement of the crushed coal and the pyrites over the surfaces of the rotating and non-rotating components also creates a critical wear problem.
The classifying or separating function in a rotating throat bowl mill is carried out at least in part by a vane wheel which comprises a plurality of circumferentially spaced and angularly pitched vanes which are secured to the rotating bowl at the outer periphery thereof and which rotate therewith. A forced air system in or associated with the mill urges air upwardly from the lower chamber through the vane wheel and thence upwardly through the housing of the bowl mill. The pyrites and heavier particles emerging radially outwardly from the crusher surface fall downwardly through the vane and contact the upper surfaces of the vane plates. The coal fines which are carried upwardly by the forced air tend to impact the lower angled surface of a deflector which lies peripherally adjacent and just above the vane wheel. It is known to use wear-resistant materials at these critical locations, see for example U.S. Pat. No. 4,605,174 issued Aug. 12, 1986 to Maliszewski et al. Stationary throat updraft pulverizers are also known. These differ essentially from rotating throat mills in that the vane wheel is attached to the outside mill wall and does not rotate with the crusher bowl.